Revert "fix: stop changing the behaviour of spies on mockFn.mockReset (…

…#13692)"

This reverts commit eace3a1.

docs/MockFunctionAPI.md

@@ -130,7 +130,7 @@ Beware that `mockFn.mockClear()` will replace `mockFn.mock`, not just reset the
 
 Does everything that [`mockFn.mockClear()`](#mockfnmockclear) does, and also removes any mocked return values or implementations.
 
-This is useful when you want to completely reset a _mock_ back to its initial state.
+This is useful when you want to completely reset a _mock_ back to its initial state. (Note that resetting a _spy_ will result in a function with no return value).
 
 The [`resetMocks`](configuration#resetmocks-boolean) configuration option is available to reset mocks automatically before each test.
 

packages/jest-mock/src/__tests__/index.test.ts

@@ -1247,30 +1247,6 @@ describe('moduleMocker', () => {
     expect(fn.getMockName()).toBe('jest.fn()');
   });
 
-  test('after mock reset, the object should return to its original value', () => {
-    const myObject = {bar: () => 'bar'};
-
-    const barStub = moduleMocker.spyOn(myObject, 'bar');
-
-    barStub.mockReturnValue('POTATO!');
-    expect(myObject.bar()).toBe('POTATO!');
-    barStub.mockReset();
-
-    expect(myObject.bar()).toBe('bar');
-  });
-
-  test('after resetAllMocks, the object should return to its original value', () => {
-    const myObject = {bar: () => 'bar'};
-
-    const barStub = moduleMocker.spyOn(myObject, 'bar');
-
-    barStub.mockReturnValue('POTATO!');
-    expect(myObject.bar()).toBe('POTATO!');
-    moduleMocker.resetAllMocks();
-
-    expect(myObject.bar()).toBe('bar');
-  });
-
   test('mockName gets reset by mockRestore', () => {
     const fn = jest.fn();
     expect(fn.getMockName()).toBe('jest.fn()');

packages/jest-mock/src/index.ts

@@ -504,7 +504,6 @@ export class ModuleMocker {
   private _mockConfigRegistry: WeakMap<Function, MockFunctionConfig>;
   private _spyState: Set<() => void>;
   private _invocationCallCounter: number;
-  private _originalFn: WeakMap<Mock, Function>;
 
   /**
    * @see README.md
@@ -517,7 +516,6 @@ export class ModuleMocker {
     this._mockConfigRegistry = new WeakMap();
     this._spyState = new Set();
     this._invocationCallCounter = 1;
-    this._originalFn = new WeakMap();
   }
 
   private _getSlots(object?: Record<string, any>): Array<string> {
@@ -771,12 +769,7 @@ export class ModuleMocker {
 
       f.mockReset = () => {
         f.mockClear();
-        const originalFn = this._originalFn.get(f);
-        const originalMockImpl = {
-          ...this._defaultMockConfig(),
-          mockImpl: originalFn,
-        };
-        this._mockConfigRegistry.set(f, originalMockImpl);
+        this._mockConfigRegistry.delete(f);
         return f;
       };
 
@@ -1225,7 +1218,7 @@ export class ModuleMocker {
         return original.apply(this, arguments);
       });
     }
-    this._originalFn.set(object[methodKey] as Mock, original);
+
     return object[methodKey] as Mock;
   }
 
@@ -1418,7 +1411,6 @@ export class ModuleMocker {
   }
 
   resetAllMocks(): void {
-    this._spyState.forEach(reset => reset());
     this._mockConfigRegistry = new WeakMap();
     this._mockState = new WeakMap();
   }